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rod should not be removed too quickly, otherwise
the suction its removal produces may pull the
sphere out with it. The position of the sphere may
only be checked using the observation holes. Never
look into the barrel!
• Before launching, ensure that no one is in the way
of the trajectory. To launch, the cord of the launch-
ing lever is given a short pull perpendicular to the
lever.
• The projectile launcher requires no maintenance
and may not be oiled or otherwise made dirty. It
may be cleaned using acetone, ethanol (white
spirit) or petroleum ether except in the vicinity of
the angle scale. Avoid dipping the equipment in
water since this may cause the spring to rust.
• The angle scale can be calibrated, for example,
after dismantling the projectile launcher. To do
this, the launcher is placed in a vertical position
(90°) and it should be observed whether a projec-
tile launched directly upwards like this falls straight
back into the aperture of the barrel (in order that
the projectile is not damaged by hitting sharp
edges, it should be stopped by hand after a short
distance). If the sphere does not fall directly back
into the barrel, the launch angle should be cor-
rected and another experiment attempted. Once
the precise vertical position is found by this means,
the securing screws for the scale can be loosened
slightly and the scale adjusted so that it shows 90°,
then it is secured firmly once again.
• The projectile launcher should be stored with the
spring loose and the knurled screw
tightened.
4. Experiment procedure and evaluation
4.1 Experiment setup
1
2
1
Fig. 2: Experiment setup, key:
Projectile launcher,
3
of projectile,
Book or board etc. 25 mm high,
6
paper,
e.g. Easel with whiteboard
•
One possible experiment setup is shown sche-
matically in Fig. 2 (not to scale). If the projectile
is to land directly on the board (or book), it should
only slightly
bm
345 6
2
Launch position
4
5
Paper,
Carbon
be noted that the launch height is y
•
When launching against a vertical wall, (e.g.
whiteboard U10030 mounted on easel U10381)
the radius of the projectile sphere (1.25 cm)
should be subtracted from the horizontal distance
from the "launch point to the wall" to obtain the
distance measurement x
ment y
is derived from the distance of the "point
M
of impact on the wall to the table top" minus
3.75 cm (2.5 + 1.25).
4.2 Experiment procedure
•
It is practical when performing experiments to
note the experiment number, the spring tension
(1, 2 or 3), the launch angle and the values x
end y
. Example:
M
No.
Spring
Launch
angle ϕ / °
tension
1
1
2
1
3
1
4
1
5
1
6
1
7
1
8
2
9
3
4.3 Experimental evaluation
•
It is practical to select the origin of the coordi-
nate system to coincide with the mid-point of the
projectile as it exits the barrel. Then:
cos ϕ
v
= v
x
0
sin ϕ
v
= v
y
0
1
=
−
y v t
gt
y
2
x = v
t
x
•
From Eq. 4 it follows that t = x / v
can be canceled out using Eq. 3
•
If the values v
x
resulting equation using Eqs. 1 and 2 then
=
ϕ
−
2
y x
tan
x
emerges as the equation for the trajectory of the
projectile. In this equation, only the initial launch
velocity v
is unknown, since distances x and y
0
have been measured during the course of the
experiments. If v
experiments, the results are as follows:
5
= 2.5 cm.
0
. The height measure-
M
Projectile
Target
distance
height
x
/ m
y
M
45
0.20
0.166
45
0.40
0.262
45
0.60
0.293
45
0.70
0.274
45
0.80
0.244
45
1.00
0.126
45
1.14
0.000
45
2.34
0.000
45
4.60
0.000
(1)
(2)
2
(3)
(4)
, where time
x
and v
are eliminated from the
y
g
(5)
2
2
ϕ
2
v
cos
0
is calculated for each of the
0
M
/ m
M
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